Mitigation of Near-Field Effects for Seismic Surface Wave Velocity Estimation with Cylindrical Beamformers
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 131, Issue 8
Abstract
Analysis of seismic surface waves offers a noninvasive method to estimate the dynamic engineering properties of the near-surface earth. Traditional two-sensor spectral analysis of surface waves (SASW) techniques suffer from several limitations that impede their use in practice, including poor resolution, inability to properly account for multiple modes, and an imprecise understanding of near-field effects. Current multichannel and array analysis of surface waves resolve several of these limitations, but still suffer from a near-field model incompatibility, i.e., estimating plane wave parameters in a cylindrically spreading wave field. This paper introduces cylindrical beamforming, an array processing method to overcome the limitations of plane wave processing methods. To aide in motivating the cylindrical beamformer, the paper discusses the near-field effects and explains some of the underlying physical reasons for previous observations regarding the near-field. The cylindrical beamformer is then introduced to more accurately model the wave field, allowing better estimates of phase velocity from point sources. The results from measured data taken with a linear array on a site in Atlanta are used to compare the methods.
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Acknowledgments
This research was supported by the National Science Foundation under Grant No. NSFCMS-9616013 and U.S. Air Force Office of Scientific Research Grant No. F49620-98-1-0233. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the writers and do not necessarily reflect the views of the National Science Foundation or the U.S. Air Force. The writers are grateful to Dr. Clifford J. Astill of the National Science Foundation and Captain Michael T. Chipley of the U.S. Air Force for their support and encouragement.
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Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 131 • Issue 8 • August 2005
Pages: 970 - 977
Copyright
© 2005 ASCE.
History
Received: Sep 23, 2003
Accepted: Sep 8, 2004
Published online: Aug 1, 2005
Published in print: Aug 2005
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